A known sheet transport assembly is applied in an inkjet printing apparatus, wherein a printing station is arranged as a process unit to apply ink on a receiving substrate, such as a sheet. The sheet transport assembly comprises a conveying unit and the printing station comprises an inkjet print head assembly. The conveying unit comprises a transport belt, such as an endless metallic belt, and several rollers arranged for transporting the endless transport belt. A sheet is arranged on the transport belt and is advanced on the transport belt in a transport direction along the printing station wherein an inkjet image is applied onto a process side of the sheet.
The inkjet image is formed by applying dots of an ink, such as an aqueous ink or a non-aqueous ink, on the sheet. In the case of aqueous ink the printed sheet becomes wet on the process side due to the aqueous ink dots. The moisture is absorbed into the sheet and enlarges the fibers of the sheet at the process side of the sheet depending on the sheet properties. As a result an internal tension grows in the sheet, and a portion of the sheet may curl downwards towards the transport belt in case the sheet is not attracted to the transport belt. This may be prevented by attracting the sheet to the transport belt. This attraction may be supplied by an electrostatic force or suction pressure provided at a contact side of the sheet on the transport belt.
The printed sheet is separated from the transport belt by applying a separation air flow to a leading edge of the sheet proximate to a deflection element, such as a roller, which deflection element deflects the transport belt. It is generally known that deflection elements having smaller radius along its deflection surface for deflecting the transport belts provide better separation than deflection elements having a bigger radius along its deflection surface. Said separation air flow is directed along the transport belt adjacent to the deflection element for lifting the leading edge of the sheet from the transport belt at the position of the deflection element. During the separation step the leading edge of the sheet is moved in flight to a next transport element, such as another transport belt. However a curled portion of the sheet being curled towards the transport belt makes it more difficult to separate the leading edge of the sheet from the transport belt. It has been found that the leading edge of the sheet may be pushed backwards at the deflection element by the separation air flow in a direction opposite to the transport direction, thereby further bending the curled portion of the sheet towards the transport belt. As a result, the sheet is not reliably separated from the transport belt, and in the case it is separated, it is not reliably moved over to a next transport element.
It is accordingly an object of the present invention to increase the reliability of separating a sheet from the transport belt, particularly if the sheet has a portion which curls towards the transport belt due to internal tension.